1. Field of the Invention
This invention relates generally to digital rebalance loops and more particularly to a high resolution, radiation-hardened digital rebalance loop for gas damped accelerometers wherein the digital rebalance loop is radiation hardened.
2. Discussion of the Prior Art
Low cost accelerometers used with laser-gyrobased systems for aircraft navigation and tactical missile applications have traditionally used an integral, vendor-supplied analog rebalance loop with an external digitizer. The existing implementations of both the analog loop and the digitizer have recognized problems in a nuclear radiation environment due to bias shifts in analog devices. Most current military applications require some level of radiation hardening.
One example of a rebalancing circuit is disclosed in U.S. Pat. No. 3,877,020 to Brunsting. Brunsting discloses an integrator type voltage to frequency converting circuit including a switchable current rebalancing source for rebalancing the input to the integrator. The rebalancing current source is controlled to provide paired transition rebalancing pulses for linear and symmetrical operation of the converter. Brunsting teaches that the rebalancing pulse must have a net polarity with the intervals of switch on being of sufficient duration to permit build up of a current to a given amplitude and the intervals of switch off being of sufficient duration to permit complete decay of the prior current. The loop is rebalanced by introducing a number of pulses directly proportional to the input analog signal applied to the integrator circuit. These pulses are applied to the integrator input of the circuit and not the torquing coil of the accelerometer itself.